"Resin" is a generic term used to describe both natural and synthetic glues which derive their adhesive properties from their inherent ability to polymerize in a consistent and predictable fashion. The vast majority of modem industrial resins are synthetic, and are normally derived from petroleum feedstocks. Two of the most important classes of synthetic resins, in terms of production volume and total sales are phenol formaldehyde (P/F) and urea formaldehyde (U/F) resins. In both cases, the principal market application is for use as a glue binder in man-made wood products.
Phenol formaldehyde (P/F) resin, because of its resistance to moisture, has a particular value in external (outdoor) or damp environments. It is therefore, the leading adhesive used for the manufacture of plywood, oriented strand board (OSB) and wafer board (Sellers, 1996). P/F resins are also widely used in laminates, insulation, foundry materials, moulding compounds, abrasives and friction materials for the transportation industry (i.e., clutch facings, disk facings and transmission components). As its name suggests, the principal ingredients in P/F adhesives are phenol and formaldehyde. However, the finished product is actually a mixture of P/F, caustic, and water. Assorted fillers, extenders and dispersion agents may then be added for specific adhesive applications.
The formaldehyde ingredient in P/F resin is derived from methanol, normally produced from natural gas. The phenol ingredient is typically manufactured from benzene arid propylene via a cumene intermediate. In addition to P/F adhesive manufacture, phenol is used in the manufacture of other important products, for example, Bisphenol A and Caprolactam. Bisphenol A is a principal component in polycarbonates used in automotive parts, compact discs and computer discs, and Caprolactam is a raw material for Nylon 6, used within stain resistant carpets.
When mixed together in water and with caustic added as a catalyst, phenol and formaldehyde undergo a condensation reaction to form either ortho- or para-methylolphenol. The resultant PF resin, as shipped to market, is a dark brown liquid which is polymerized and cross-linked to an intermediate degree. It is then cured in the final board, laminate or other product without catalyst simply with the addition of heat at which time the final polymerization and cross-linking take place via condensation reactions. The release of free formaldehyde during the resin manufacture and resin use stages is a concern from a health and safety perspective. Furthermore, the costs associated with formaldehyde production have increased and there is a need in the art for alternative materials for use as wood adhesives and binders.
One alternative for phenol that has been considered are lignins which have been recovered from wood, wood residues, bark, bagasse and other biomass via industrial or experimental processes. Natural lignin (i.e. the polymer which occurs in nature which holds wood and bark fibres together and gives wood its strength) and P/F formaldehyde resins are structurally very similar. Lignin is a random network polymer with a variety of linkages, based on phenyl propane units. Lignin-based adhesive formulations have been tested for use within plywood, particle board and fibre board manufacture. The addition of polymeric lignin to P/F formulations has been found to prematurely gel the P/F resin thereby reducing shelf life, limiting permeation of the lignin-P/F resin into the wood and producing an inferior mechanical bond (Kelley 1997). It is important to note that lignins which are isolated and recovered from biomass, and which have been tested in resin formulations, are not identical to the natural lignin present in the original biomass, but are altered somewhat by the recovery process. Some examples of recovered lignins which have been tested in PF resin formulations are Kraft lignin, lignosulphonates, Alcell.TM., Organocell.TM., pyrolytic lignin and natural resin of the present invention.
Pyrolysis of lignin has been considered as a potential approach to upgrading lignin to more usable phenolic type resins. While relatively mild thermal or thermo-catalytic processing at low pressures can be used to break the lignin macromolecules into smaller macromolecules, lignin segments and monomeric chemicals, such procedures may cause condensation reactions producing highly condensed structures such as char and tar, rather than depolymerized lignin fragments or monomeric chemicals.
A further alternative for the production of phenolic compounds involves use of pyrolytic pitch oils produced in the rapid destructive distillation (fast pyrolysis) of wood and other biomass. These pyrolytic oils are comprised of a complex mixture of compounds including phenolic compounds, guaiacol, syringol and para substituted derivatives, carbohydrate fragments, polyols, organic acids, formaldehyde, acetaldehyde, furfuraldehyde and other oligomeric products (Pakdel et al 1996). However, wood-derived lignin and lignin-rich pyrolytic bio-oils have lacked consistency and have exhibited inferior properties when compared with phenol-formaldehyde resins (Chum et al. 1989; Scott 1988; Himmelblau 1997; Kelley et al., 1997).
Due to the complexity of pyrolytically-derived bio-oils, further processing is required in order to obtain suitable fractions useable as a replacement for phenol, or to be considered as an extender for petroleum-derived phenol within P/F resin formulations. Typically the phenolic derived from pyrolysis oils requires separation prior to use in order to remove impurities. One such method involves water extraction of the whole-oil, followed by precipitation and centrifugation or filtration and drying of the non-aqueous fraction to prepare a "pyrolytic lignin" fraction (Scott 1988). However, adhesive formulations prepared using pyrolytic lignin were found to be inferior to P/F resin formulations in both colour and odour, and required long press times in order to avoid de-lamination of waferboards. Tests indicated that none of the pyrolytic lignin samples meet the internal bond (IB) test requirement (Scott 1988, see pp. 91-92).
In U.S. Pat. No. 4,209,647 (Jun. 24, 1980) a fractionation method for the preparation of a phenol-enriched pyrolytic oil is disclosed which involved a multistep process that selectively solubilized neutral phenols, and organic acids of the whole-oil with NaOH followed by extraction with methylene chloride. However, this multistep process is costly, laborious, time consuming and involves the use of volatile solvents that are known to be health threatening.
Another fractionation method involves adding ethyl acetate to whole-oil pitch to produce ethyl acetate soluble and insoluble fractions. The ethyl soluble fraction is then isolated and the ethyl acetate evaporated to isolate a fraction containing phenolic and neutrals (P/N) derived from the pyrolytic oil (Chum et al. 1989, U.S. Pat. No. 4,942,269, Jul. 17, 1990, and U.S. Pat. No. 5,235,021, Aug. 10, 1993). Preliminary results with the P/N fractions revealed that fractionated pyrolytic oils could be used within P/F resin compositions, as P/N containing resins exhibited equivalent gel times as noted for P/F resins. However, the fractionation protocol is not suitable for industrial scale production, nor is this process cost effective for the preparation of alternative components for use within P/F resins at a commercial scale (Kelley et al., 1997).
All of the process disclosed within the prior art as outlined above involve the extraction of a phenol-enhanced fraction from the whole pyrolytic oil product using complex protocols involving precipitation, followed by centrifugation or filtration, or the use of solvents and alkali. None of the prior art discloses methods for the production of a bio-oil which is readily prepared from the whole pyrolytic oil or that exhibits properties suitable for adhesive use. Furthermore, the prior art does not disclose methods directed at producing a fraction of bio-oil suitable for adhesive use, yet that is simple to produce and that does not require any solvent extraction.
It is an object of the invention to overcome disadvantages of the prior art.
The above object is met by the combinations of features of the main claims, the sub-claims disclose further advantageous embodiments of the invention.